I also found a thread about your issue, and it said that when you start MSFS, do not start in administrator mode, just left click on your icon to start it in normal mode. I have to do this myself, so it does work, at least for me.
Thank You Marcus for this release. I have been so surprised with the lack of new releases information coming out of FS Expo this weekend, and then to see this. This is definitely the highlight of this weekend! As a beta tester for Marcus, I definitely encourage EVERYONE to check this scenery out. You won't be disappointed! I'm not going to compare it to Orbx or Megascenery, or any other addon....you just have to see it for yourself. What an amazing addon Marcus, and thank you for the "gift"